Radio base station apparatus and radio communication method

ABSTRACT

The fading correlation monitor  103  detects an angle spread of the communication terminal apparatus  200 - 1  and decides whether the angle spread has a larger or smaller relationship with a preset threshold value. When the estimated angle spread is smaller than the threshold value, the interference wave is suppressed by carrying out directive reception which is carried out by an AAA receiver  106  as well as performing directive transmission which is carried out in a transmitting circuit  122 .While, when the estimated angle spread is larger than the predetermined value, the distortion of the signals due to the fading is compensated by carrying out diversity receiving which is carried out in a diversity receiver  107  as well as performing diversity transmission which is carried out in a diversity transmitter  123 .On account of this, even when the fading correlation is small, it is possible to carry out a radio communication with a satisfactory communication quality.

TECHNICAL FIELD

The present invention relates to a radio base station apparatus and aradio communication method for directional transmission and reception.

BACKGROUND ART

In digital radio communication, adaptive array antenna (hereinafter,referred to as “AAA”) technology which adaptively controls thedirectivity of a plurality of antenna elements by adding weight to theantenna output is used. In the AAA technology, it is possible tosuppress the interfering waves by adaptively controlling the directivityutilizing the fact that the directions of arrival of signals aredifferent from each other. Accordingly, the AAA technology is preferredas a method for suppressing the interfering waves.

Referring to FIG. 1, the formation of directivity pattern in a radiobase station apparatus which utilizes the AAA technology will bedescribed. FIG. 1 is a diagram showing a transmitted radio wave which istransmitted from a communication terminal apparatus arrives at a radiobase station apparatus provided by two antenna elements.

The radio wave transmitted from communication terminal apparatus isreceived by radio base station apparatus via its respective antennaelements 31 and 32. In this case, the received radio wave 34 which isreceived by the antenna element 32 introduces a larger phase rotationcompared with the received radio wave 33 which is received by theantenna element 31, since the former travels through path difference Llonger than that of the latter.

The radio base station apparatus monitors and measures the differencebetween the phase rotation of the received radio wave 33 and the phaserotation of the received radio wave 34 (difference in phase rotation).Since the difference in phase rotation and the direction of arrival ofthe received radio wave always related to each other when the fadingcorrelation is high, the radio base station apparatus estimates thedirection of arrival of the received radio wave based on the measureddifference in phase rotation, and generates a directivity pattern forsuppressing the multi-path and other users interference.

However, when the fading correlation between the received radio wave 33and the received radio wave 34 is small and therefore the fading itselfto which the received radio wave 33 and the received radio wave 34 aresubjected to in the respective paths is different, the difference inphase rotation measured by the radio base station apparatus includes notonly the difference due to the difference in the travelling paths butalso the difference due to the difference of the fading itself.Consequently, when the fading correlation is small, the difference inphase rotation measured by the radio base station apparatus and thedirection of arrival of the received radio wave do not always related toeach other. Thus, since the direction of arrival (direction of angle .in FIG. 1) of the received radio wave can not be estimated correctlywhen the fading correlation is small, there exists a problem thatdesired directivity can not be correctly generated leading todeterioration of the communication quality.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a radio base stationapparatus and a radio communication method capable of carrying out radiocommunication with a satisfactory communication quality even when thefading correlation is small.

This object can be achieved by carrying out diversity transmission andreception without generating the directivity so that the distortion ofthe signal due to fading is compensated and the communication quality isimproved even when the fading correlation of the respective receivedwaves is small.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a transmitted radio wave which istransmitted from a communication terminal apparatus arrives at a radiobase station apparatus provided by two antenna elements;

FIG. 2 is a diagram illustrating a base station apparatus according to afirst embodiment of the present invention;

FIG. 3 is a block diagram illustrating the base station apparatusconfiguration according to the first embodiment of the presentinvention;

FIG. 4 is a block diagram illustrating the configuration of a fadingcorrelation monitor according to the first embodiment of the presentinvention;

FIG. 5 is a diagram showing an example of an adder output according tothe first embodiment of the present invention;

FIG. 6 is a block diagram illustrating the configuration of a fadingcorrelation monitor according to a second embodiment of the presentinvention;

FIG. 7 is a block diagram illustrating the configuration of a fadingcorrelation monitor according to a third embodiment of the presentinvention;

FIG. 8 is a block diagram illustrating the configuration of a fadingcorrelation monitor according to a fourth embodiment of the presentinvention; and

FIG. 9 is a block diagram illustrating the configuration of a fadingcorrelation monitor according to a fifth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

When the fading correlation is small and the fading environments of aplurality of antennas are different, then performance deterioration dueto the fading can be reduced by carrying out transmission using anantenna that is capable of performing transmission of signals under aslight distortion of the signals caused by fading. Accordingly, in thecase of small fading correlation, diversity technologies are preferred.In these diversity technologies, the diversity receiving technology isan art that compensates the distortion of the signals caused by fading,at the receiving side, the uncorrelated received signals of a pluralityof branches are appropriately combined. On the other hand, the diversitytransmission technology is an art that compensates in advance, thedistortion of the signals caused by fading before transmitting thesignals by appropriately combining the transmission signals of aplurality of branches at the transmitting side.

While, when the fading correlation is high and therefore the directionof arrival can be estimated correctly, it is possible to remove theinterference between communicating parties of which direction of arrivalis different by means of directive transmission and directive reception.However, to improve the communication quality in case of a high fadingcorrelation, the AAA technology is preferred.

While considering the performing of a satisfactory radio communicationas a main point, it is essential of the present invention to suppressthe interference wave by carrying out directional transmission/receptionwhen a monitored fading correlation is larger than a predeterminedthreshold value, and to compensate the distortion of the signals due tofading by carrying out diversity transmission/reception when the fadingcorrelation is smaller than a predetermined threshold value.

Referring to the attached drawings, a detail description of theembodiments of the present invention is given below.

(First Embodiment)

In a first embodiment, the case when the fading correlation is detectedby monitoring the angle spread will be explained while directing theviewpoint to the fact that the larger the angle spread is the smallerfading correlation. That is to say, in order to carry out radiocommunication with a satisfactory communication quality, the basestation apparatus according to the first embodiment estimates the anglespread based on the received signal, and when the estimated angle spreadis smaller than a predetermined threshold value, it carries out the AAAtransmission and reception to suppress the interference wave whilecarrying out diversity transmission and reception to compensate thedeterioration of the signal when the angle spread is larger than apredetermined threshold value.

FIG. 2 is a diagram illustrating a base station apparatus according tothe first embodiment of the present invention.

The radio wave transmitted from the radio base station apparatus 100 isscattered by the obstacles such as buildings etc surrounding thecommunication terminal apparatuses 200-1 to 200-3 which in turn intendedto receive the scattered signal. Moreover, the radio waves transmittedfrom the communication terminal apparatuses 200-1 to 200-3 are scatteredby the same surrounding obstacles as the reception case and are receivedby the radio base station apparatus 100. Herein, the scattering circles201-1 to 201-3 denote imaginary circles drawn around the respectivecommunication terminal apparatuses 200-1 to 200-3 to represent thelocation where the obstacles which scatter the transmitted/receivedradio wave of the communication terminal apparatuses 200-1 to 200-3exist. Further, 0.1 to 0.3 denote, respectively, the angle spreadobtained by drawing two tangent lines from the radio base stationapparatus 100 to the respective scattering circles 201-1 to 201-3.

FIG. 3 is a block diagram illustrating the configuration of the basestation apparatus 100.

The base station apparatus 100 has transmitting/receiving circuits 100-1to 100-3 corresponding to the respective communication terminalapparatuses 200-1 to 200-3. The transmitting/receiving circuit 100-1includes a fading correlation monitor 103, a switch 104, an arrivaldirectivity estimator 105, an AAA receiver 106, a diversity receiver107, a demodulator 114, a modulator 120, a switch 121, an AAAtransmitter 122 and a diversity transmitter 123. Since thetransmitting/receiving circuits 100-1 to 100-3 have the sameconfiguration, the description will be restricted only to thetransmitting/receiving circuit 100-1 as an example, and the descriptionof the transmitting/receiving circuits 100-2 to 100-3 will be omitted.

The radio receivers 102-1 to 102-3 carry out a (predetermined) known ora normal radio reception processing such as down-conversion, etc., onthe signals received by the corresponding antennas 101-1 to 101-3, andoutput the received signals which have been radio reception processed tofading correlation monitor 103, switch 104 and arrival directivityestimator 105.

The fading correlation monitor 103 detects the angle spread 0.1 of thecommunication terminal apparatus 200-1 based on the received signal,takes a decision on the angle spread whether it is larger or smallerthan a preset threshold value, and outputs a switching signal thatindicates the decision result to both switch 104 and switch 121.Hereinafter, the decision on large/small relationship relative to thepreset threshold value will be referred to as “threshold valuedecision”.

The switch 104 outputs the signals received from the radio receivers toeither the AAA receiver 106 or to the diversity receiver 107 accordingto the switching signal. The arrival directivity estimator 105 estimatesthe direction of arrival of the received signals and outputs the resultof estimation to the AAA receiver 106 provided by weight calculator 111and to AAA transmitter 122 provided by weight calculator 131.

When the received signals are outputted from the switch 104, the AAAreceiver 106 calculates the weights based on the result of theestimation of direction of arrival in the arrival directivity estimator105 so as to suppress the interference wave in the uplink, and weightsthe received signals of the respective branches with the respectivecalculated weights. In the AAA receiver 106, the weight calculator 111decides the weight by which each received signal branch is multipliedbased on the result of estimation of the direction of arrival. Themultipliers 112-1 to 112-3 multiply the received signal of therespective branch by its respective weight calculated in the weightcalculator 111. The adder 113 captures and adds up the multiplicationresults received from the multipliers 112-1 to 112-3 and outputs theadded result to the demodulator 114.

When the received signals are outputted from the switch 104, thediversity receiver 107 processes the received signal of the respectivebranches with the maximal-ratio combining to compensate the distortionof the received signal due to the fading in the uplink. Themaximal-ratio combining technique is a combing technique by which thereceived signals of the respective branches which have been weightedproportionally to the received power and inverse proportionally to thenoises are added constructively. Further, the diversity receiver 107 mayuse the equal-gain combining technique in which the received signals ofrespective branches are added directly without being weighted, or it mayuse the selection combining technique in which the received signal thathas the maximum estimated received power among all of the receivedsignals of the respective branches is selected, etc.

The demodulator 114 demodulates the output of the AAA receiver 106 orthe output of the diversity receiver 107 with a predetermineddemodulating mode such as QPSK, etc., and obtains the received data.

The modulator 120 modulates the transmission data with a predeterminedmodulating mode, and outputs the modulated signal to the switch 121. Theswitch 121 outputs the transmission signal outputted from the modulator120 to either the AAA transmitter 122 or to the diversity transmitter123 based on the switching signal outputted from the fading correlationmonitor 103.

When a transmission signal is outputted from the switch 121, the AAAtransmitter 122 calculates the weights based on the result of theestimation of the direction of arrival estimated in arrival directivityestimator 105 so as to suppress the interference wave in the downlink,and weights the transmission signals of the respective branches with thecalculated weights. In AAA transmitter 122, the weight calculator 131decides the weight by which each received signal is multiplied based onthe result of the estimation. The multipliers 132-1 to 132-3 multiplythe transmission signals of the respective branches by their respectiveweights calculated in the weight calculator 131.

When the transmission signal is outputted from the switch 121, thediversity transmitter 123 carries out the maximal-ratio combining on thetransmission signals of the respective branches referring to theweighting in the diversity receiver 107 to previously compensate thedistortion of the transmission signal due to the fading in the downlink(maximal-ratio diversity transmission). Further, the diversitytransmitter 123 may use selective diversity transmission which selectsonly the received signal that has the maximum estimated received powerdepending on the combining mode in the diversity receiver 107, or mayuse closed loop type (feed back type) diversity transmission thatselects the weighting of the transmission signal or transmission antennaaccording to information received from the mobile station (feed backinformation), etc.

The radio transmitters 141-1 to 141-3 carry out a predetermined radiotransmission processing on the transmission signals outputted from thecorresponding multipliers 132-1 to 132-3 or the diversity transmitter123, and transmit the radio processed signals via the correspondingantennas 101-1 to 101-3.

The directive reception and directive transmission carried out in theforegoing AAA receiver 106 and AAA transmitter 122, respectively, arepreferable when the fading correlation of the respective branches of thereceived signals is large, while the diversity reception and diversitytransmission carried out in the diversity receiver 107 and diversitytransmitter 123, respectively, are preferable when the fadingcorrelation of the respective branches of the received signals is small.

FIG. 4 is a block diagram illustrating the configuration of a fadingcorrelation monitor 103 according to the first embodiment of the presentinvention.

The memory 151 memorizes the received signals outputted from the radioreceivers 102-1 to 102-3, and outputs the memorized received signals tothe multipliers 153-1 to 153-3 of the corresponding branch every timewhen the weight sequentially generator 152 outputs the weight. Thememory 151 memorizes the received signals until the switching signalcorresponding to the received signals is generated in the thresholdvalue deciding section 156. The weight sequentially generator 152generates the weights that can produce a directivity pattern of 0°–360°in 1° increment, and outputs the weights to the multipliers 153-1 to153-3. The multipliers 153-1 to 153-3 multiplies the received signals ofthe respective branches which are output from the memory 151 by theweights outputted from the weight sequentially generator 152, andoutputs the multiplication result to the adder 154. The adder 154 addsup the outputs of the multipliers 153-1 to 153-3 and outputs theresultant to the angle spread estimator 155. The angle spread estimator155 which outputs a 1° increment directivity pattern measures theresultant corresponding output power of the adder 154, and estimates theangle spread based on the measurement result. The threshold valuedeciding section 156 carries out threshold value decision process on theangle spread estimated in the angle spread estimator 155, and outputsthe switching signal that represents the decision result to both switch104 and switch 121.

An operational explanation of the base station apparatus 100 configuredas described above is given below.

The radio waves transmitted from the communication terminal apparatuses200-1 to 200-3 are scattered by the obstacles existing on the peripheryof the corresponding scattering circles 201-1 to 201-3, and are receivedby the radio base station apparatus 100.

In the base station apparatus 100, the signals transmitted from thecommunication terminal apparatuses 200-1 to 200-3 are received viaantennas 101-1 to 101-3. The received signals are subjected to apredetermined radio reception processing operation and are output tofading correlation monitor 103, switch 104 and arrival directivityestimator 105.

Now, an operational description of the fading correlation monitor 103 isgiven below.

In the fading correlation monitor 103, the angle spread of the partnercommunication terminal apparatus is estimated based on the receivedsignal of the respective branches, the estimated angle spread issubjected to threshold value decision process, then a switching signalis generated to indicate either the AAA receiver 106 or the diversityreceiver 107 is to process the received signal.

The received signals of the respective branches which have beenprocessed by a predetermined radio reception processing in the radioreceivers 102-1 to 102-3 are memorized in the memory 151, and areoutputted from the memory 151 to the corresponding multipliers 153-1 to153-3 synchronizing to the output timing of the weight sequentiallygenerator 152. The received signals of the respective branches memorizedin the memory 151 are multiplied by the weights corresponding to thedirectivity pattern of 0°–360°, which are outputted from the weightsequentially generator 152 in 1° increment, added to each other andoutputted to the angle spread estimator 155. That is to say, thereceived power being formed with the directivity of 0°–360° is outputtedto the angle spread estimator 155.

In the angle spread estimator 155, the received signals weighted so asto form the directivity of 0°–360° and outputted from the adder 154, aremeasured in 1° (precision) increment, and the measured powers aresubjected to threshold value decision process. This threshold valuedecision process is carried out to measure the angle spread of thepartner communication terminal apparatuses 200-1 to 200-3. When themeasured power is larger than a threshold value which means that thereceived radio wave comes from that direction what “that direction”,then, it is decided that a scattering circle exists in that direction.On the contrary, when the measured power is smaller than the thresholdvalue which means that the received radio wave does not come from thatdirection what “that direction”, then, it is decided that a scatteringcircle does not exist in that direction. Further, the estimation methodof the angle spread is not limited to this, and it is changeabledepending on the system.

FIG. 5 shows an example of the addition results measurement which isoutputted from the adder 154.

As shown in the figure, since the measured power is larger than thethreshold value, (p), between 0.1 and 0.2, then, it is decided that ascattering circle exists between 0.1 and 0.2. The absolute range|0.1-0.2| where it is decided that the scattering circle exists isestimated as the angle spread. The estimated angle spread |0.1-0.2| isoutputted to the threshold value deciding section 156.

In the threshold value deciding section 156, a threshold value has beenset previously and the angle spread which is estimated in the anglespread estimator 155 is subjected to threshold value decision processutilizing the previously set threshold value. While taking intoconsideration the fact that the larger the angle spread is the smallerfading correlation, then, the threshold value decision process iscarried out in order to decide either AAA receiver 106 or diversityreceiver 107 is to process the received signal, and accordingly, todecide either AAA transmitter 122 or diversity transmitter 123 is toprocess the transmission signal. In other words, when the estimatedangle spread is smaller than the threshold value which means that thefading correlation is large then, it is decided that the received signaland the transmission signal are to be processed, respectively, by theAAA receiver 106 and the AAA transmitter 122. On the contrary, when theestimated angle spread is larger than the threshold value, then it isdecided that the received signal and the transmission signal are to beprocessed, respectively, by the diversity receiver 107, and thediversity transmitter 123. By this way of carrying out the thresholdvalue decision process, a switching signal that represents the result ofthe threshold value decision process is generated. The generatedswitching signal is output to the switch 104 and switch 121. Thethreshold value is appropriately set in the system taking intoconsideration the location of the obstacles that scatters the receivedradio wave, the algorithm for calculating the weight, etc.

In the switch 104, the received signal is outputted to either AAAreceiver 106 or diversity receiver 107 according to the switching signaloutputted from the fading correlation monitor 103. The received signalsof the respective branches outputted to the AAA receiver 106 aremultiplied by the respective weights so as to suppress the interferencewave, and are demodulated in the demodulator 114 resulting in thereceived data. Whereas the received signals of the respective branchesoutputted to the diversity receiver 107, are processed withmaximal-ratio combining so that the distortion due to the fading iscompensated, and are demodulated in the demodulator 114 resulting in thereceived data.

On the other hand, in the switch 121, the transmission signal, which hasbeen modulated in the modulator 120, is outputted to either AAAtransmitter 122 or diversity transmitter 123 according to the switchingsignal outputted from the fading correlation monitor 103 Thetransmission signals outputted to the AAA transmitter 122, aremultiplied by the respective weights so as to suppress the interferencein the downlink, and are processed with a predetermined radiotransmission processing such as up-conversion, etc., in the radiotransmitters 141-1 to 141-3, and are transmitted via antennas 101-1 to101-3. The transmission signals of the respective branches outputted tothe diversity transmitter 123, are maximal-ratio combining processed soas to compensate the distortion due to the fading in the downlink,subjected to radio transmission processing such as up-conversion in theradio transmitters 141-1 to 141-3, and are transmitted via antennas101-1 to 101-3.

Thus, according to the first embodiment, the angle spread is estimatedbased on the received signal, and when the estimated angle spread issmaller than a predetermined threshold value, the interference wave issuppressed by carrying out the AAA transmission and reception and whenthe angle spread is larger than the threshold value, the distortion ofthe signal due to the fading is compensated by carrying out thediversity transmission and reception, therefore, it is possible to carryout a radio communication with a satisfactory (may be sufficient)communication quality.

Further, according to the first embodiment, since the scatteringradiuses are roughly of the same size, it is understood that the largerthe angle spread is the smaller distance between the base stationapparatus and the communication terminal apparatus. Accordingly, whenthe angle spread is larger than the predetermined threshold value, thediversity transmission and reception is carried out and the transmittingpower is reduced to a low level. On account of this, the influence ofthe interference on the other stations can be reduced without using anyadaptive array antenna.

Furthermore, according to the first embodiment, when the received signalis processed in the diversity receiver 107 under the control of theswitch 104, the arrival directivity estimator 105 does not have to carryout estimation of the direction of arrival. Therefore, the powerconsumption can be reduced.

(Second Embodiment)

The base station apparatus according to a second embodiment calculates afading correlation value among the respective antenna elements, and whenthe calculated fading correlation value is larger than a predeterminedthreshold value, the interference wave is suppressed by carrying out theAAA transmission and reception while carrying out the diversitytransmission and reception to compensate the distortion due to fadingwhen the calculated fading correlation value is smaller than thethreshold value, and hence, a radio communication with a satisfactorycommunication quality is carried out. That is to say, the secondembodiment is different from the first embodiment in the point that thefading correlation among the respective antenna elements is monitored bycalculating the fading correlation value itself.

FIG. 6 is a block diagram illustrating the configuration of a fadingcorrelation monitor 103 according to the second embodiment of thepresent invention. Next, the base station apparatus according to thesecond embodiment will be described referring to the FIG. 6. Further,according to the second embodiment, since the configuration of the basestation apparatus excluding the fading correlation monitor 103 is thesame as that of the base station apparatus according to the firstembodiment, the detailed description will be omitted.

The complex operator 251 obtains a complex conjugates of S1, S2 and S3,which are the received signals of the respective branches outputted fromthe radio receivers 102-1 to 102-3, and outputs the obtained complexconjugates to the correlation detector 252. S1, S2, and S3, are thereceived signals outputted from the radio receivers 102-1, 102-2, and102-3, respectively. Furthermore, the complex conjugate of S1, S2, andS3, are designated, respectively, as S1*, S2* and S3*.

In the correlation detector 252, the fading correlation value iscalculated using the complex conjugates S1*, S2* and S3* of the receivedsignals of the respective branches outputted from the complex operator251 and the received signals S1, S2 and S3 of the respective branches.That is to say, the correlation value of the received signals S1 and S2is S1×S2*, the correlation value of the received signals S1 and S3 isS1×S3* and the correlation value of the received signals S2 and S3 isS2×S3*, then, all correlation values are added up to obtain the fadingcorrelation value. The correlation detector 252 outputs the fadingcorrelation value calculated in this manner to the threshold valuedeciding section 253.

The threshold value deciding section 253 carries out threshold valuedecision process on the fading correlation value outputted from thecorrelation detector 252, and outputs a switching signal whichrepresents the decision result to the switch 104 and the switch 121.

Now, an operational description of the base station apparatus 100configured as described above is given below.

The received signals, which have been received from the antennas 101-1to 101-3, are subjected to a predetermined radio reception processing inthe radio receivers 102-1 to 102-3, and outputted to the fadingcorrelation monitor 103, the switch 104 and the arrival directionestimator 105. In the fading correlation monitor 103, the calculatedfading correlation value is subjected to the threshold value decisionprocess, and accordingly a switching signal is generated.

An operational description of the fading correlation monitor 103 isgiven below.

In the fading correlation monitor 103, the fading correlation valueamong the respective antenna elements is calculated based on thereceived signals of the respective branches, the calculated fadingcorrelation value is subjected to threshold value decision process, andcorresponding to the result of the decision process, a switching signalis generated to indicate either AAA receiver 106 or diversity receiver107 is to process the received signal.

The received signals S1, S2 and S3 of the respective branches areoutputted to the complex operator 251 and the correlation detector 252.In the complex operator 251, the complex conjugates S1*, S2* and S3* ofthe received signals of the respective branches are obtained. The S1*,S2* and S3* are outputted to the correlation detector 252 and multipliedby the received signals S1, S2 and S3, then the multiplication resultsare added together to produce the fading correlation value.

The fading correlation value is then subjected to the threshold valuedecision operation in the threshold value deciding section 253. Thethreshold value decision operation is carried out corresponding to thefading correlation value in order to take a decision on the receivedsignals that should be processed by either AAA receiver 106 or diversityreceiver 107 moreover, to decide that either AAA transmitter 122 ordiversity transmitter 123 should process the transmission signal. Inother words, when the fading correlation value obtained by thecorrelation detector 252 is larger than a threshold value, it isdetermined that the received signals are processed by the AAA receiver106 and the transmission signals are processed by the AAA transmitter122. On the contrary, when the fading correlation value is smaller thanthe threshold value, it is decided that the received signals areprocessed by the diversity receiver 107 and the transmission signals areprocessed by the diversity transmitter 123.

Furthermore, the switching signal which represents the result of thethreshold value decision process is generated and outputted to theswitch 104 and the switch 121. The threshold value is appropriately setin the system taking into account the location of the obstacles thatscatters the received radio wave, the algorithm for calculating theweight, etc.

Thus, according to the second embodiment, the fading correlation valueis calculated based on the received signals, and when the calculatedfading correlation value is smaller than a predetermined thresholdvalue, the interference wave is suppressed by carrying out the AAAtransmission and reception, and when the angle spread is larger than thepredetermined threshold value, the distortion of the signal due to thefading is compensated by carrying out the diversity transmission andreception, and hence, a radio communication with a satisfactorycommunication quality can be carried out.

Further, in the second embodiment, it is understood that the smaller thefading correlation value is the smaller distance between the basestation apparatus and communication terminal apparatus. Accordingly,when the fading correlation value is smaller than a predeterminedthreshold value, the diversity transmission and reception is carriedout, and the transmitting power can be suppressed to a lower level. Onaccount of this, the influence of interference on the other stations canbe reduced without using any adaptive array antenna.

(Third Embodiment)

Examples in which the AAA transmission/reception and the diversitytransmission/reception are switched over according to the distancebetween the base station apparatus and a communication terminalapparatus are given in third, fourth and fifth embodiments. That is tosay, in the third embodiment, while taking into consideration the factthat the distance between the base station apparatus and thecommunication terminal apparatus can be estimated in accordance with theelectric power of the received signal, the AAA transmission/receptionand the diversity transmission/reception are switched over according tothe received power. In the fourth embodiment, while taking intoconsideration the fact that the distance between the base stationapparatus and communication terminal apparatus can be estimatedaccording to the time lag (difference in timing) between the receivingtiming of the received signal and the transmitting timing of thetransmission signal, the AAA transmission/reception and the diversitytransmission/reception are switched over there between. In the fifthembodiment, however, tacking into consideration the fact that thedistance between the base station apparatus and the communicationterminal apparatus can be estimated according to the number of the TPCinformation bits, the AAA transmission/reception and the diversitytransmission/reception are switched over there between.

The base station apparatus according to the third embodiment estimatesthe distance between its own apparatus and the partner communicationterminal apparatus based on the received power of the received signal,and when the estimated distance is larger than a predetermined thresholdvalue, it carries out the AAA transmission and reception to suppress theinterference wave, while, carrying out the diversity transmission andreception to compensate the distortion of the signal due to the fadingwhen the estimated distance is smaller than the predetermined thresholdvalue. That is to say, the third embodiment is different from the firstembodiment in the point that the fading correlation between therespective antenna elements is monitored based on the distance betweenthe base station apparatus and the communication terminal apparatus.

FIG. 7 is a block diagram illustrating the configuration of a fadingcorrelation monitor 103 according to the third embodiment of the presentinvention. Referring to FIG. 7, an operational description of the basestation apparatus according to the third embodiment is given below.Further, since the structure of the base station apparatus according tothe third embodiment excluding the fading correlation monitor 103 is thesame as that of the base station apparatus according to firstembodiment, detailed description thereof will be omitted.

The received power calculators 301-1 to 301-3 calculate the electricpower of the signals received from the corresponding radio receivers102-1 to 102-3, and outputs the calculated electric power to thethreshold value deciding section 302. The threshold value decidingsection 302 adds up the received power outputted from the received powercalculators 301-1 to 301-3. Then, the added received power is subjectedto the threshold value decision process and a switching signal thatrepresents the decision result is outputted to the switch 104 and theswitch 121.

Next, an operational description of the base station apparatus 100configured as described above is given below.

The signals received via antennas 101-1 to 101-3 are subjected to apredetermined radio reception processing in the radio receivers 102-1 to102-3, and are outputted to the fading correlation monitor 103, theswitch 104 and the arrival direction estimator 105. In the fadingcorrelation monitor 103, the calculated received power is subjected tothe threshold value decision process and accordingly, a switching signalis generated.

An operational description of the fading correlation monitor 103 isgiven below.

In the fading correlation monitor 103, the electric power of thereceived signals of the respective branches is calculated, and thecalculated electric power is subjected to the threshold value decisionprocess, then a switching signal is generated, according to the decisionresult, so as to decide either AAA receiver 106 or diversity receiver107 is to process the received signal.

First, in the received power calculators 301-1 to 301-3, the electricpowers of the received signals of the respective branches outputted fromthe radio receivers 102-1 to 102-3 are calculated. The calculatedreceived powers are added up in the threshold value deciding section302, and the addition result is then subjected to the threshold valuedecision process.

Referring to the fact that the larger the addition result of thereceived powers of the respective branches is the smaller fadingcorrelation and since the base station apparatus and communicationterminal apparatus are close to each other, the threshold value decisionprocess is carried out in order to decide that the received signalsshould be processed either by the AAA receiver 106 or by the diversityreceiver 107 and to decide also that the transmission signal should beprocessed either by the AAA transmitter 122 or by the diversitytransmitter 123. That is to say, when the addition result of thereceived powers is smaller than a threshold value and hence, the fadingcorrelation is large, it is decided that the AAA receiver 106 processesthe received signals and the AAA transmitter 122 processes thetransmission signals. While it is decided that the received signals areprocessed by the diversity receiver 107, and the transmission signalsare processed by the diversity transmitter 123 when the addition resultof the received power is larger than the threshold value.

Moreover, the switching signal that represents the result of thethreshold value decision process is generated and then outputted to theswitch 104 and the switch 121. The threshold value is appropriately setin the system taking into account the location of the obstacles thatscatters the received radio wave, the algorithm for calculating theweight, etc.

As described above, according to the third embodiment, when the electricpower of the received signal is larger than a predetermined thresholdvalue, the interference wave is suppressed by carrying out the AAAtransmission and reception, and when the electric power of the receivedsignal is smaller than the predetermined threshold value, the distortionof the signal due to the fading is compensated by carrying out thediversity transmission and reception, and therefore, it is possible tocarry out radio communication with a satisfactory communication quality.

Further, in the third embodiment, it is understood that the larger thereceived power, the closer the distance between the base stationapparatus and communication terminal apparatus. Accordingly, when thereceived power is larger than a predetermined threshold value, thediversity transmission and reception is carried out, and thetransmitting power can be suppressed to a lower level. On account ofthis, the influence of interference on the other stations can be reducedwithout using any adaptive array antenna.

(Fourth Embodiment)

The base station apparatus according to the fourth embodiment estimatesthe distance between its own apparatus and the partner communicationterminal apparatus based on the time lag of the transmitting timingbetween the receiving timing of the receive signal and the transmittingtiming of the transmission signal. When the estimated distance is largerthan a predetermined threshold value, the AAA transmission and receptionis carried out to suppress the interference wave while when theestimated distance is smaller than the predetermined threshold value,the diversity transmission and reception is carried out to compensatethe distortion of the signals due to the fading. That is to say, thefourth embodiment is different from the third embodiment in the pointthat the former estimates the distance between the base stationapparatus and communication terminal apparatus based on the time lagbetween the receiving timing of the received signal and the transmittingtiming of the transmission signal.

FIG. 8 is a block diagram illustrating the configuration of a fadingcorrelation monitor 103 according to the fourth embodiment. Referring toFIG. 8, an operational description of the base station apparatusaccording to the fourth embodiment is given. Furthermore, since thestructure of the base station apparatus according to the fourthembodiment excluding the fading correlation monitor 103 is the same asthe base station apparatus of the first embodiment, detailed descriptionthereof will be omitted.

The timing detector 401 detects the time difference between the inputtime of the received signal and the input time of the transmissionsignal, and outputs the detected time difference to the threshold valuedeciding section 402. The threshold value deciding section 402 carriesout threshold value decision process on the time difference outputtedfrom the timing detector 401, and then outputs a switching signal whichrepresents the decision result to the switch 104 and the switch 121.

Now, an operational description of the base station apparatus 100configured as described above is given.

The signals received via antennas 101-1 to 101-3 are subjected to thepredetermined radio reception processing in the radio receivers 102-1 to102-3, and outputted to the fading correlation monitor 103, the switch104 and the arrival directivity estimator 105. In the fading correlationmonitor 103, the calculated received power is subjected to the thresholdvalue decision process to generate the switching signal.

Now, an operational description of the fading correlation monitor 103 isgiven.

In the fading correlation monitor 103, the electric powers of thereceived signals of the respective branches are calculated, thecalculated electric powers are subjected to the threshold value decisionprocess, and the switching signal which decides that the receivedsignals should be processed by either the AAA receiver 106 or thediversity receiver 107 is generated according to the decision result.

First, in the timing detector 401, the time difference between the inputtime of the received signal and the input time of the transmissionsignal is detected.

The detected time difference is subjected to the threshold valuedecision process in the threshold value deciding section 402. Referringto the fact that the larger the time difference between the receivedsignal and the transmission signal is, the longer distance between thebase station apparatus and communication terminal apparatus and hence, asmaller fading correlation, the threshold value decision process iscarried out to decide that the received signals should be processedeither by the AAA receiver 106 or the diversity receiver 107 and todecide also that the transmission signals should be processed either bythe AAA transmitter 122 or the diversity transmitter 123. That is tosay, when the time difference is larger than the threshold value andhence, the fading correlation is large, it is decided that the receivedsignals are processed by the AAA receiver 106 and the transmissionsignals are processed by the AAA transmitter 122. While it is decidedthat the received signals are processed by the diversity receiver 107and the transmission signals are processed by the diversity transmitter123 when the time difference is smaller than the threshold value.

The switching signal that represents the result of the threshold valuedecision process is generated and outputted to the switch 104 and theswitch 121. The threshold value is appropriately set in the systemtaking into account the location of the obstacles that scatters thereceived radio wave, the algorithm for calculating the weight, etc.

As described above, according to the present embodiment, when the timedifference is larger than a predetermined threshold value, theinterference wave is suppressed by carrying out the AAA transmission andreception, and when the electric power of the received signal is smallerthan a predetermined threshold value, the distortion of the signal dueto the fading is compensated by carrying out the diversity transmissionand reception, and hence, it is possible to carry out a radiocommunication with a satisfactory communication quality.

Further, in the fourth embodiment, it is understood that the smaller thetime difference is the smaller distance between the base stationapparatus and communication terminal apparatus. Accordingly, when thetime difference is smaller than a predetermined threshold value, thediversity transmission and reception is carried out, and thetransmitting power can be reduced to a lower level. On the account ofthis, the interference that influences other stations can be reducedwithout using any adaptive array antenna.

(Fifth Embodiment)

The base station apparatus according to a fifth embodiment estimates thedistance between its own apparatus and the partner communicationterminal apparatus based on the TPC-bits information used for up/downconversion of the transmission power in transmission power controllingprocess. When the estimated distance is larger than a predeterminedthreshold value, the AAA transmission and reception is carried out tosuppress the interference wave, and when the estimated distance issmaller than the predetermined threshold value, the diversitytransmission and reception is carried out to compensate the distortionof the signals due to the fading. That is to say, the fifth embodimentis different from the third embodiment in the point that the formerestimates the distance between the base station apparatus andcommunication terminal apparatus based on the TPC-bits.

FIG. 9 is a block diagram illustrating the configuration of a fadingcorrelation monitor 103 according to the fifth embodiment. Referring tothe FIG. 9, an operational description of a base station apparatusaccording to the fifth embodiment is given below. Further, since thestructure of the base station apparatus according to the fifthembodiment excluding the fading correlation monitor 103 is the same asthe base station apparatus of the first embodiment, detailed descriptionthereof will be omitted.

The TPC bit extracting section 501 extracts the TPC bits included in thereceived signals and outputs the extracted TPC-bits to the thresholdvalue deciding section 502. In the threshold value deciding section 502,the number of the bits used for raising up the transmitting power(hereinafter, referred to as “up-information bits”) is counted out ofthe total TPC bits output from the TPC bit extracting section 501, thenumber of the counted up-information bits is subjected to the thresholdvalue deciding process, and a switching signal that represents thethreshold value is outputted to the switch 104 and the switch 121.

Next, an operational description of the base station apparatus 100configured as described above is given.

The signals received via antennas 101-1 to 101-3 are subjected to thepredetermined radio reception processing in the radio receivers 102-1 to102-3, and outputted to the fading correlation monitor 103, the switch104 and the arrival direction estimator 105. In the fading correlationmonitor 103, the calculated received powers are subjected to thethreshold value deciding process to generate the switching signal.

An operational description of the fading correlation monitor 103 isgiven below.

In the fading correlation monitor 103, the electric powers of thereceived signals of the respective branches are calculated, thecalculated electric powers are subjected to the threshold value decisionprocess, and the switching signal which decides that the receivedsignals should be processed either by the AAA receiver 106 or thediversity receiver 107 is generated according to the decision result.

First, in the TPC bit extracting section 501, TPC bits are extractedfrom the received signals, then the extracted TPC bits are outputted tothe threshold value deciding section 502.

In the threshold value deciding section 502, the number of the bits thatindicate the raising up of the transmitting power (up-information bits)are counted out of the total TPC bits outputted from the TPC bitextracting section 501, and the counted bit number is subjected to thethreshold value decision process. While considering the fact that thelarger number of the up-information bits is the worse condition of thepropagation path, and hence, a smaller fading correlation, the thresholdvalue decision process is carried out in order to decide that thereceived signals should be processed by either the AAA receiver 106 orthe diversity receiver 107 and to decide also that the transmissionsignals should be processed by either the AAA transmitter 122 or thediversity transmitter 123. That is to say, when the number of theup-information bits is smaller than the threshold value, and hence thefading correlation is large, it is decided that the received signals areprocessed by the AAA receiver 106 and the transmission signals areprocessed by the AAA transmitter 122. On the contrary, when the upinstruction bits is larger than the threshold value, then, it is decidedthat the received signals are processed by the diversity receiver 107and the transmission signals are processed by the diversity transmitter123.

The switching signal that represents the result of the threshold valuedecision process is generated and outputted to the switch 104 and theswitch 121. The threshold value is appropriately set in the systemtaking into account the location of the obstacles that scatters thereceived radio wave, the algorithm for calculating the weight, etc.

Thus, according to the fifth embodiment, when the number of theup-information bits is larger than a predetermined threshold value, theinterference wave is suppressed by carrying out the AAA transmission andreception, while when the electric power of the received signal issmaller than the predetermined threshold value, the distortion of thesignal due to the fading is compensated by carrying out the diversitytransmission and reception, and therefore, it is possible to carry out aradio communication with a satisfactory communication quality.

Further, in the fifth embodiment, since the larger number of theup-information bits is the worse propagation path environment, it isunderstood that the mobile station is located in a faraway position fromthe base station. Accordingly, when the number of the up-informationbits is larger than a predetermined threshold value, the diversitytransmission and reception is carried out, and the transmitting powercan be reduced to a lower level. On account of this, the interferencethat influences other stations can be reduced without using any adaptivearray antenna.

Furthermore, in the respective embodiments described above, the case inwhich the maximal-ratio combining diversity transmission is carried outhas been mainly described as a method of the diversity transmission,however, it is needless to say that other methods of diversitytransmission are also applicable. For example, satisfactory transmissioncharacteristics can be achieved when a selective transmission or aclosed loop type diversity transmission is adopted.

As demonstrated in the foregoing descriptions, according to the presentinvention, radio communication with a satisfactory communication qualitycan be carried out even when the correlation of the fading is small bymonitoring the fading correlation, then by switching over the AAAtransmission/reception and the diversity transmission/receptionaccording to the monitoring result.

This application is based on the Japanese Patent Application No.2000-197133 filed on Jun. 29, 2000. The entire content thereof isincorporated herein.

INDUSTRIAL APPLICABILITY

The present invention is preferably applicable to both a radio basestation apparatus and a radio communication method which carry outdirectional transmission and reception.

1. A radio base station apparatus comprising: a fading correlationmonitor that detects a fading correlation of radio waves receivedthrough a plurality of antenna elements; a reception method selectorthat receives the radio waves from the antenna elements and provides theradio waves to a receiver selected in accordance with the detectedfading correlation; a directional receiver that executes directionalreception, on the provided radio waves, only when the reception methodselector selects the directional receiver to receive the provided radiowaves; a diversity receiver that executes diversity reception, on theprovided radio waves, only when the reception method selector selectsthe diversity receiver to receive the provided radio waves; and ademodulator that demodulates a signal output by the receiver selected toreceive the radio waves provided by the reception method selector,wherein: the directional receiver creates directivity for the radiowaves to increase the quality of the demodulated signal, and thediversity receiver combines or selects a plurality of signal sequenceswithin the radio waves to increase the quality of the demodulatedsignal.
 2. The radio base station apparatus of claim 1 wherein thereception method selector selects the directional receiver to receivethe provided radio waves when the detected fading correlation is greaterthan a predetermined threshold value and selects the diversity receiverto receive the provided radio waves when the fading correlation is lessthan or equal to the predetermined threshold value.
 3. The radio basestation apparatus of claim 1, further comprising: a transmission methodselector that receives a modulated signal and provides the modulatedsignal to a transmitter selected in accordance with the detected fadingcorrelation; a directional transmitter that executes directionaltransmission, on the provided modulated signal, through the antennaelements only when the transmission method selector selects thedirectional transmitter to transmit the provided modulated signal; adiversity transmitter that executes diversity transmission, on theprovided modulated signal, through the antenna elements only when thetransmission method selector selects the diversity transmitter totransmit the provided modulated signal, wherein: the directionaltransmitter creates directivity for the provided modulated signal usingthe antenna elements, and the diversity transmitter combines or selectsfor transmission a plurality of signal sequences within the providedmodulated signal.
 4. The radio base station apparatus of claim 3,wherein the transmission method selector selects the directionaltransmitter to transmit the provided modulated signal when the fadingcorrelation is greater than a predetermined threshold value and selectsthe diversity transmitter to transmit the provided modulated signal whenthe fading correlation is less than or equal to the predeterminedthreshold value.
 5. The radio base station apparatus of claim 3,wherein, the diversity transmitter transmits at a lower transmissionpower than the directional transmitter.
 6. The radio base stationapparatus of claim 1, wherein the fading correlation monitor estimatesan angle spread of a signal received from a communicating party anddetects the fading correlation with reference to the estimated anglespread.
 7. The radio base station apparatus of claim 1, wherein thefading correlation monitor calculates a fading correlation value anddetects the fading correlation with reference to the calculated fadingcorrelation value.
 8. A radio communication method comprising: detectinga fading correlation of radio waves received through a plurality ofantenna elements; providing the received radio waves to a receiverselected in accordance with the detected fading correlation; executingdirectional reception, on the provided radio waves, with a directionalreceiver only when the directional receiver is selected to receive theprovided radio waves; executing diversity reception, on the providedradio waves, with a diversity receiver only when the diversity receiveris selected to receive the provided radio waves; and demodulating asignal output by the receiver selected to receive the provided radiowaves, wherein: executing directional reception creates directivity forthe provided radio waves to increase the quality of the demodulatedsignal, and executing diversity reception combines or selects aplurality of signal sequences within the provided radio waves toincrease the quality of the demodulated signal.
 9. The radiocommunication method of claim 8, further comprising: providing amodulated signal to a transmitter selected in accordance with thedetected fading correlation; executing directional transmission, for theprovided modulated signal, through the antenna elements with adirectional transmitter only when the directional transmitter isselected to transmit the provided modulated signal; executing diversitytransmission, for the provided modulated signal, through the antennaelements with a diversity transmitter only when the diversitytransmitter is selected to transmit the provided modulated signal,wherein: the directional transmitter creates directivity for theprovided modulated signal using the antenna elements, and the diversitytransmitter combines or selects for transmission a plurality of signalsequences within the provided modulated signal.